The invention relates to an orthodontic expansion screw for the generation of an expansion force between oppositely lying sides of the upper jaw, according to the generic term of patent claim 1.
The use of such expansion screws is well known in orthodontics. Expansion screws serve for the palatal suture widening for the skeletal widening of the upper jaw. Expansion screws of the type mentioned are disclosed, for example, in the patent documents WO-97/15241 A1; EP 0 706 349 B1; and U.S. Pat No. 4,045,871. In general, an expansion screw comprises a first and a second fastening elements to be fastened to oppositely lying sides of the upper jaw, and an adjusting element connected with these, by means of which the reciprocal spacing of the fastening elements is adjustable. For the anchoring of the fastening elements to oppositely lying teeth of the upper jaw there serve as a rule mounting wires. for the anchoring onto the teeth there is used in each case a mounting wire with two free ends per fastening unit.
Especially in patients of advanced age, the expansibility of the palatal suture decreases, and considerable forces must be applied in order to achieve any expansion at all. There, great forces act on the expansion screw and forces as well as torques act on the mounting wires which not infrequently bend in an undesired manner under the load, so that the effect of the expansion screw is lessened or entirely lost.
Underlying the invention, therefore, is the problem higher loads and with which an increased force effect can be exerted on the upper jaw for the expansion, without deformation of the mounting wires.
This problem is solved by the features given in claim 1.
According to the invention, each fastening element has at least two mounting wires with at least three free ends for the anchoring to teeth of the upper jaw.
Therewith there is yielded the advantage that per fastening element there are available at least three, preferably however, four anchoring points on the upper jaw, whereby the achievable force and torsional action on the upper jaw and the loadability of the expansion screw are altogether increased. There, the structure form o the fastening element and on/f the adjusting element is not the essential feature. These parts can be present in any known or novel construction form.
Further embodiment and modifications of the invention are yielded for the dependent patent claims.
Thus the mounting wires of each fastening element are preferably arranged at mutual spacing from one another on the respective fastening element. The mounting wires can be arranged adjacently or also one over another on the respective fastening element.
The in each case like-aligned free ends of the mounting wires in the starting state are directed about parallel to the longitudinal axis of the expansion screw. They can also be directed, however, about perpendicularly to the longitudinal axis of the expansion screw.
So that the expansion screw, especially the transition between the fastening elements and he mounting wires, will withstand heavy loads, the mounting wires are advantageously joined firmly with the fastening elements by welding, soldering or clamping.